What is near field and far field in Electromagnetics

[narayani]

Dear Sir,
Can you explain me, what is near field and far field in electromagnetics.

 

[desert_eagle]

Reactive near-field regionis defined as that portion of the near-field region immediately surrounding the antenna wherein the reactive field predominates. For most antennas, the outer boundary of this region is commonly taken to exist at a distance R< 0.62*sqrt(D^3/λ)from the antenna surface, where λ is the wavelength and D is the largest dimension of the antenna.

Far-field (Fraunhofer) regionis defined as “that region of the field of an antenna where the angular field distribution is essentially independent of the distance from the antenna. If the antenna has a maximum overall dimension D, the far-field region is commonly taken to exist at distances greater than 2D^2/λ from the antenna.
You can study for more in a book Antenna theory and design of C.A Balanis.

 

[narayani]

Can you explain me near field and far field at the static electric charge or simple magnet. I have doubt, when static electric charge, which is having near and far filed region, similarly for magnetic.
Can you clear these doubts.

 

[PlanarMetamaterials]

Hi narayani,

For simple static charges, there is no propagation, and the above definitions don't really apply (lambda -> infinity). Therefore, we typically say that there is no far-field region, and everything behaves like the near field.